Syria (Monday 28th May, 2012) - Rebels in Syria are partly responsible for the massacre of more than 100 people in the town of Houla, Russian Foreign Minister Sergei Lavrov says.

Mr Lavrov, whose government a close ally of the Syrian regime, said some victims had been killed at close range in a district controlled by rebels.

The UN condemned the killings, saying government artillery was involved.

UN-Arab League envoy Kofi Annan has arrived in Damascus for talks on implementing his peace plan.

He called on "every individual with a gun" to lay down their arms.

"I have come to Syria at a critical moment in this crisis," Mr Annan said shortly after his arrival.

"I am personally shocked and horrified by the tragic incident in Houla."

At a joint news conference with UK counterpart William Hague in Moscow, Mr Lavrov said that Russia was "deeply alarmed" by the massacre in Houla.

"We are dealing with a situation in which both sides evidently had a hand in the deaths of innocent people," he said.

"There is no doubt that the government used artillery and tanks and this has been reported by UN observers who have visited the scene.

"There is also no doubt that many bodies have been found with injuries from firearms received at point-blank range. So the blame must be determined objectively."

He said the causes of the massacre must be understand so that it could never be repeated.

Asked if President Bashar al-Assad could be part of the solution in Syria, he said that ending the violence was more important than who was in power.

"We do not support the Syrian government. We support the plan of Kofi Annan," he said.

The Syrian government insists the killings were carried out by "terrorists".

Analysts earlier expressed surprise at Russia's support for the UN Security Council condemnation of the Houla killings. Moscow has so far been reluctant to apportion any blame for deaths in Syria to the Assad regime.